HAM Radio 3/hamradioversion3.0examsandprograms1992.iso/news/inham89/1055.

Text File | 1979-12-31 | 10KB | 242 lines

INFO-HAMS Digest            Thu, 21 Dec 89       Volume 89 : Issue 1055

Today's Topics:
                      ARRL NR 91: HF DATA FILING
    pudgy wound helical antenna (60m vertical in my living room!)
                        QST misinformation...
                    W1AW: Computer-generated QRM ?
----------------------------------------------------------------------

Date: 21 Dec 89 05:00:47 GMT
From: samsung!cs.utexas.edu!asuvax!stjhmc!f1.n234.z1.fidonet.org![e-mail],
Subject: ARRL NR 91: HF DATA FILING
Message-ID: <[e-mail]>

 > Message-ID: <[e-mail]>
 >
 > ARRL BULLETIN 91 (ARLB091) 12/15/89
 >
 > ON DECEMBER 12, ARRL COUNSEL CHRIS IMTAY, N3AKD, FILED A PETITION
 > FOR RULE MAKING WITH FCC SEEKING THE ADOPTION OF RULES TO PERMIT
 > LIMITED HF RTTY AND DATA COMMUNICATION UNDER AUTOMATIC CONTROL.

Bravo!! Thanks for the good news.

73 de W8GRT



--
Uucp: ...{gatech,ames,rutgers}!ncar!asuvax!stjhmc!234!1!Jim.Grubs,.W8GRT
Internet: Jim.Grubs,[e-mail]

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Date: 22 Dec 89 01:38:29 GMT
From: [e-mail]  (Mike Smith)
Subject: pudgy wound helical antenna (60m vertical in my living room!)
Message-ID: <[e-mail]>

In article <[e-mail]> [e-mail] (Tim Bagwell) writes:
>> Yes it is possible to resonate out the capacitive reactance of the short antenna
>> by a lumped or distributed inductance but what you end up with is usually a
>> very small radiation resistance! This means that the ratio  of radiation
>> resistance to "ohmic" resistance drops and you loose your power to heat.
>> In ship board MF antennas the radiation resistance is often less than a on
>> ohm! (Moral of the story: Use thick wire or tube for short antennas!)
>
>True and another reason why a small diameter helical antenna is worse than
>a simple vertical of comparable height and wire size.

Ah, but by how much is it worse?

Ummm, but I'm not transmitting.  Im, well, umm, one of those SWL folks
who like to listen ....  Since efficiency isn't as important as SN ratio
for a reciever why do I care?  Yeah, I will have a little less signal,
but that isn't nearly as much of a problem as finding a place to put
up a 31 meter (or 60 meter!) vertical ...

Per _The ARRL Antenna Book_ page 6-18 heading 'Short Helically Wound
Vertical Antennas'

    Shortened quarter-wavelength vertical antennas can be made by
    forming a helix on a long cylindrical insulator.  The diameter
    of the helix must be very small in terms of wavelength in order
    to prevent the antenna from radiating in the the axial mode.
    Acceptable form diameters for HF-band operations are from 1 inch
    to 10 inches when the practical aspects of antenna construction
    are considered.

Looks to me like 4" diameter is in the reasonable range.  The diameter
should be small in terms of wavelength, so I would expect that for
a 31 meter band antenna even using a 1 meter diameter would be OK;
though with some increased tendency for 'high angle radiation' as
the mode of radiation starts to shift from broadside to axial.
Though it does say 'very small' so maybe 1/30th isn't very small...

And further on:

    No strict rule has been established concerning how short a
    helically wound vertical can be before a significant drop in
    performance is experienced.  As a general recommendation, one
    should use the greatest amount of length consistent with
    available space.  A guideline might be to maintain an element
    length of 0.05 wavelength or more for antennas which are
    electrically a quarter wavelength long.  Thus, use 13 feet or
    more of stock for an 80-meter antenna, 7 feet for 40 meters,
    and so on.

This works out to 5 feet for a 31 meter antenna, so a 4 foot length
should still be OK unless there is some profound non-linearity that
isn't mentioned... Though I must admit that adding a loading coil to
it for use on 60 meters was clearly a bit of whimsey and would be
subject to loading coil losses.  (But it was fun, though!)

and:

    No specific rule exists concerning the size or type of wire one
    should use in making a helix.  Larger wire sizes are, or course,
    preferable in the interest of minimizing I**2R losses in the
    system.  For power levels up to 1000 watts it is wise to use
    a wire size of of no. 16 or larger.

Since I'm using it as a recieving antenna I don't have much 'I' to
square and I would expect that no. 16 wire would be serious overkill.
It doesn't look like copper tubing is needed.

They then go on to discuss the use of an L network to match the low
impedance (which they say is on the order of 5 ohms - I still need to
figure out how to properly measure mine with the antenna bridge...) and
show a practical antenna design for 7 MHz with 2:1 SWR over 50 kHz.
(NOT pudgy wound though...).

(There is also the mention of using helically wound ground plane
 elements for the counterpoise, but that is another discussion)

In summary, I don't contest your observations; they are quite true.
The numbers need to be looked at to see if they are important.

I think that the above quotes are evidence that, with a matching
network, the effects you describe are not significant for an antenna
used for recieving the 31 meter band that is 4 feet long and 4" in
diameter; and are probably not important for transmitting if no. 16
or larger wire were used.

What do you think?  Have I missed something in my interpretation of
what they have presented as fact?  Are their rules of thumb off base?


--

E. Michael Smith  [e-mail]

'Whatever you can do, or dream you can, begin it.  Boldness has
 genius, power and magic in it.'  -  Goethe

I am not responsible nor is anyone else.  Everything is disclaimed.

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Date: 21 Dec 89 14:43:44 GMT
From: zaphod.mps.ohio-state.edu!usc!cs.utexas.edu!asuvax!stjhmc!f670.n142.z1.fidonet.org![e-mail]  (Luck Hurder)
Subject: QST misinformation...
Message-ID: <[e-mail]>

All de KY1T:

There's a bit of misinformation going around that I'd
like to set straight, folks.  A USENET user (?), perhaps
N8DGN, I can't be sure, has been saying the following here
on the echo:

  > They (the ARRL) are now changing their tune where microwave
  > coverage in QST is concerned.  It is not acceptable to
  > ENTIRELY DROP microwave coverage from QST as they have
  > done.

QST has done no such thing.  They have merely dropped one column.
They fully intend to continue publishing any and all acceptable
articles regarding microwave that come their way.

  > I wasn't asking for the ARRL to increase their microwave
  > coverage, just to include some in QST

Which is precisely what they are doing...
  > Paul Rinaldo, who is the editor of QST, made the decision
  > to CUT ALL microwave coverage

False. Wrong. Uh-uh, no way.  This guy isn't reading the letter
that Paul wrote very well...

  > I cannot accept his decision to TOTALLY CUT
  > ALL microwave coverage.

Hey, I wouldn't accept that either, if I were an ARRL member,
which I am.  Fact is, no such decision was made.

Once again - QST will publish articles that relate to microwave
activity as they always have done, provided that the articles
make it through the article-review process that all authors
must endure, and provided that the articles meet the normal
standards.  Those standards, by the way, appear
in the January issue of QST for all to see.  No secrets here,
simply normal, every-day public knowledge..
To put things in a different light for a second, I could squack
up a storm too, if I so chose.  The same financial dilemma that
forced the microwave column to go that-a-way was also responsible
for my Public Service column to be cut by a whole page every
month.  Public Service, traffic handling, and such were -- by
the way -- the things that the ARRL were FOUNDED on.  If I
were to run around screaming that QST had dropped coverage
of public service activities, I'd be laughted out of the office!
Particularly with a FIVE pager coming up in the February issue
relating to the public service efforts of the many hundreds
of amateurs during the aftermath of Hurricane Hugo.

Enough soapbox.  73 de KY1T




--
Uucp: ...{gatech,ames,rutgers}!ncar!asuvax!stjhmc!142!670!Luck.Hurder
Internet: [e-mail]

------------------------------

Date: 21 Dec 89 23:01:29 GMT
From: hpl-opus!hpnmdla![e-mail]  (Alan Bloom)
Subject: W1AW: Computer-generated QRM ?
Message-ID: <[e-mail]>

Perry Scott asked why W1W doesn't listen before they transmit bulletins
and code practice.  I was a W1AW operator many years ago, so perhaps I can
reply.

The problem is that they transmit on all ham bands 160 thru 2 meters
simultaneously.  It would take an army of operators to listen to each
frequency before each transmission.  They switch between CW RTTY and
phone frequencies dozens of times each day to maintain the published
schedule, so you can see the impracticality of listening on each freq.

The other problem is what to do if the frequency is in use.  If the users
refuse to move, you either have to transmit on top of them (which could
be construed as intentional interference, a violation of the rules) or
try to change frequency.  The latter option would make it difficult for
W1AW's listeners to find the station when needed.

The times and frequencies are published in advance.  I realize not too
many of us have the W1AW schedule memorized, but many/most CW operators
are aware of the W1AW frequencies and try to avoid them.  On phone, the
bulletins only take a few minutes to send, so the interference is
minimized.  I am of the opinion that not too many people listen to W1AW
bulletins on phone anyway, so ARRL should just eliminate them.

Al N1AL

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End of INFO-HAMS Digest V89 Issue #1055
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